Core for absorbent articles and method of making the same

ABSTRACT

An absorbent core is provided for use in an absorbent article. The core includes a plurality of substantially continuous and coextensive filaments. At least some of the filaments have disposed on a surface thereof a layer comprising a superabsorbent material formed in place on the surface from a liquid superabsorbent polymer.

FIELD OF THE INVENTION

This invention relates to absorbent articles. More particularly, itrelates to absorbent cores for absorbent articles wherein the corecomprises an expanded tow having on its surface a superabsorbentpolymer.

BACKGROUND OF THE INVENTION

The use of absorbent articles, such as protective undergarments, hasincreased steadily for many years. Early uses, such as diapers forbabies and sanitary products for women, have in recent years been joinedby an increasing demand for products designed to deal with incontinenceissues for adults, frequently brought on by advanced age, obesity, or avariety of medical conditions. At the same time, markets have grown inall of these areas for both disposable and reusable products, dependingon the preferences of the consumer.

Currently available absorbent articles usually include superabsorbentpolymers (SAP). These materials are capable of absorbing a largequantity of body fluid, such as urine, blood, and menses, and thus havebecome the standard for absorbent articles for hygiene purposes.

One example of the use of SAP is described in U.S. Pat. No. 5,641,561 toHansen et al. There are described absorbent composites made of fibrousmaterial (e.g. cellulosic or synthetic material) and particulatesuperabsorbent polymers that are bound to the fiber via hydrogen bondingbinder molecules. Superabsorbent polymer particles are mixed asparticles with bleached kraft fluff, heated and spread out to dry. Thebinder adheres the SAP particles to the fibers. The dried product isthen fed through a hammermill and shunted to an airlay line to produce aweb containing 40% SAP particles attached to individual fibers.

U.S. Pat. No. 5,593,399 to Tanzer discloses an absorbent article, namelya diaper, having two layers attached by an adhesive to provide attachedzones and unattached zones to form pocket regions. Tanzer describes theuse of SAP particles located within the pocket regions of the article toprovide an absorbent laminate. The pocket regions are arranged in anon-contiguous and labyrinth configuration.

There is an ever-increasing demand for thinner absorbent articles thatnonetheless have high fluid absorption capacity. Unfortunately, someconventional absorbent articles tend to be bulky.

Whitmore et al., in U.S. Pat. No. 6,417,425, describe absorbent articlesincluding an absorbent core and an acquisition layer designed to affordrapid uptake of fluid, good transfer properties, good uptake uponrepeated insults with fluid, and good skin compatibility. Theacquisition layer, which also has absorbent capabilities, is prepared bya process that includes spraying onto a fibrous web a blend containingsuperabsorbent polymer particles, superabsorbent-forming monomer,initiator and water, and subjecting the web to polymerizationconditions. In the '425 patent, there is stated the belief that theabsorbent structure performs well as an acquisition layer in adisposable diaper because the swelling of the superabsorbent polymerparticles is capable of expanding the fibrous web, so that theinterstitial pore volume of the web increases after an insult of liquid.

Despite the foregoing developments, however, there remains a need forimproved absorbent articles.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an absorbent core is providedfor use in an absorbent article. The core includes a plurality ofsubstantially continuous and coextensive filaments, at least some of thefilaments having disposed on a surface thereof a layer comprising asuperabsorbent material formed in place on the surface from a liquidsuperabsorbent polymer.

According to another aspect of the invention, a method of making anabsorbent core for use in an absorbent article is provided. The methodincludes expanding a tow comprising a plurality of substantiallycontinuous and coextensive filaments, each filament having a surface.The method also includes forming, from a liquid superabsorbent polymer,a layer comprising a superabsorbent material on the surface of at leastsome of the filaments.

According to yet another aspect of the invention, a system is providedfor making an absorbent core for use in an absorbent article. The systemincludes means for applying a liquid superabsorbent polymer to a towcomprising a plurality of substantially continuous and coextensivefilaments, thereby forming a treated expanded tow comprising a liquidsuperabsorbent polymer coating on the surface of at least some of thefilaments. Means is provided for forming, from the liquid superabsorbentpolymer coating, a layer comprising a superabsorbent material on thesurface of at least some of the filaments.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a side view of an embodiment of a tow material configured toform a component of an absorbent core according to an aspect of thisinvention.

FIG. 2 is a side view of the tow material shown in FIG. 1 after it hasbeen expanded according to an aspect of this invention.

FIG. 3 is a side view of the expanded tow material shown in FIG. 2 withtreated and untreated filaments.

FIG. 4 is a schematic representation of an embodiment of a system forforming an absorbent core according to an aspect of this invention.

FIG. 5 is a schematic representation of another embodiment of a systemfor forming an absorbent core according to an aspect of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

In one exemplary aspect, the invention provides an absorbent core foruse in an absorbent article. The core comprises a plurality of filamentsin the form of an expanded tow, and a layer comprising a superabsorbentmaterial on surfaces of the filaments. In another exemplary aspect, theinvention provides method of making an absorbent core for use in anabsorbent article. The method includes providing a tow comprising aplurality of filaments, partially separating the filaments to afford anexpanded tow, and providing a layer comprising a superabsorbent materialon surfaces of the filaments.

Absorbent cores according to one exemplary embodiment of the inventionmay find particular utility in the preparation of absorbent articlessuch as protective undergarments. These may include, for example,protective underwear, training pants, adult briefs, diapers,incontinence pads, and feminine hygiene pads. The absorbent articles maybe disposable, or the cores may be disposable items removablyincorporated in re-usable articles.

Absorbent cores according to one exemplary embodiment of the inventionare pulpless and therefore less bulky. In addition, the use of expandedtow instead of pulp may advantageously afford a softer, more flexibletexture, providing a more cloth-like, comfortable feel for the wearer.

The invention will next be illustrated with reference to the figures,wherein the same numbers indicate the same elements in all figures. Suchfigures are intended to be illustrative rather than limiting and areincluded herewith to facilitate the explanation of the presentinvention. The figures are not to scale, and are not intended asengineering drawings.

Referring in general to FIGS. 1-5, an absorbent core 210 is provided foruse in an absorbent article. The core 10, 110, 210 includes a pluralityof substantially continuous and coextensive filaments 12, 112, 212, atleast some of the filaments 218 having disposed on a surface thereof alayer comprising a superabsorbent material formed in place on thesurface from a liquid superabsorbent polymer.

The filaments 12, 112, 212 can be selected from RAYON, celluloseacetate, polypropylene, polyethylene, polyethylene terephthalate, andsheath-core bi-component filaments, for example, and combinationsthereof. At least some of the filaments 12, 112, 212 can includecellulose acetate, and the surface of at least some of the filaments canbe hydrophilized. Substantially all of the filaments 218 optionally havedisposed on the surface thereof the layer comprising the superabsorbentmaterial.

The absorbent core 210 optionally includes two or more adjacent andcoextensive strata, wherein one stratum includes filaments 218 havingdisposed on the surface thereof the layer comprising the superabsorbentmaterial, and another stratum is substantially free of superabsorbentmaterial (e.g., filaments 212). The stratum that is substantially freeof superabsorbent material optionally includes a surfactant disposed onthe surface of at least some of the filaments.

Where the core 210 is provided with two opposing sides, thesuperabsorbent material is optionally disposed in a pattern on one orboth of the opposing sides. The core 210 optionally includes pulp fibersinterspersed between at least some of the filaments 12, 112, 212, andsuperabsorbent polymer particles are optionally interspersed among atleast some of the filaments 12, 112, 212.

In an exemplary method of making an absorbent core 210 for use in anabsorbent article, tow 10 is expanded and a layer comprising asuperabsorbent material is formed on the surface of at least some of thefilaments 12, 112, 212.

The forming step is optionally performed by applying to the expanded tow110 the liquid superabsorbent polymer to form a treated expanded towcomprising a liquid superabsorbent polymer coating, followed by curingthe treated expanded tow to form the layer comprising the superabsorbentis material. The applying step is optionally performed by immersing theexpanded tow 110 in a bath 44 holding the liquid superabsorbent polymer,removing the expanded tow 110 from the bath 44, and removing a portionof the liquid superabsorbent polymer coating. The applying stepalternatively includes spraying liquid superabsorbent polymer on atleast one surface of the expanded tow 110. The curing step can beaccomplished by exposing the treated expanded tow to heat or toradiation.

The step of forming a layer of superabsorbent material can be completedby patternwise spraying liquid superabsorbent polymer on one or both ofthe sides of the tow 110 or by spraying the liquid superabsorbentpolymer on one of the sides and applying a surfactant to at least someof the filaments on the other side.

The filaments 12, 112, 212 can be partially separated to form theexpanded tow 110 by, for example, blowing the tow 10 with jets of air.The tow can also be at least partially flattened. After thelayer-forming step, one or both of water and residual volatile reactantscan be removed from the formed layer. Also, the filaments can betenderized.

Pulp fibers and/or superabsorbent polymer particles are optionallyinterspersed between at least some of the filaments 12, 112, 212, and atleast some of the filaments 12, 112, 212 can be hydrophilized. Theforming step optionally includes forming a layer on selected filaments218 or on substantially all of the filaments.

According to yet another aspect of the invention, a system is providedfor making an absorbent core 210 for use in an absorbent article. Thesystem includes means, such as a bath 44 or a spray nozzle 50, 52, forapplying a liquid superabsorbent polymer to a tow 10 comprising aplurality of substantially continuous and coextensive filaments 12, 112,212, thereby forming a treated expanded tow comprising a liquidsuperabsorbent polymer coating on the surface of at least some of thefilaments. Means 46, such as a heater or radiation source, is providedfor forming, from the liquid superabsorbent polymer coating, a layercomprising a superabsorbent material on the surface of at least some ofthe filaments.

Where the core includes two opposing sides, and the means for applyingoptionally includes a spray nozzle 50, 52 configured to apply the liquidsuperabsorbent polymer on one or both of the sides in a pattern. Meanscan also be provided for applying a surfactant to the expanded tow 110.

Means 45 are optionally provided for removing a portion of the liquidsuperabsorbent polymer coating, for interspersing pulp fibers between atleast some of the filaments, for interspersing superabsorbent polymerparticles between at least some of the filaments, for flattening the tow(e.g., fiber spreader 42), for partially separating filaments of the tow(e.g., jets of air formed by air jet 43), for removing one or both ofwater and residual volatile reactants from the formed layer (e.g., dryer47), and for tenderizing the filaments (e.g., tenderizing unit 48).

Referring now to FIG. 1, there is shown a side cross section view oftow, generally Indicated at 10, suitable for use in practicing oneexemplary aspect of the invention. The tow 10 comprises a plurality offilaments 12 that are substantially continuous and coextensive. Betweenthe filaments 12 are small interstitial spaces 14. Such tow 10 may beformed from RAYON, cellulose acetate, polypropylene, polyethylene,polyethylene terephthalate, or any other polymeric material known in theart, for example sheath-core bi-component filaments.

To improve coating of a liquid superabsorbent polymer (to be describedlater) onto tow 10 comprising otherwise hydrophobic filaments such asfor example polypropylene, polyethylene, and polyethylene terephthalate,the filaments may be hydrophilized. This may be done for example bytreatment with silica, treatment with a material which has a suitablehydrophilic moiety and is not readily removable from the filament, or bysheathing the nonwettable, hydrophobic filament with a hydrophilicpolymer during or after the formation of the filament. Alternatively,the surface of the filaments may be treated with for example a coronadischarge, to afford surface hydrogen-bondable groups and therebyincrease hydrophilicity.

A combination of these filament types may also be used, and may beintermixed or layered. In some cases, it may be advantageous to use bothhydrophilic and hydrophobic filaments, in order to control thedistribution of liquid superabsorbent polymer to certain filaments (thehydrophilic ones), as is well as to exert control over the flow of urineor other body fluids in the core when used. The exemplary filaments mayhave a denier per filament of between 3 and 1000 grams/9000 m,preferably between about 10 and about 70 grams/9000 m. A combination offilament deniers may also be used, and may be intermixed or layered. Theexemplary filaments may be shaped to increase loft, for example by flator helical crimping. The filaments are substantially independent of eachother; that is, they are not bonded together to any significant degree.

FIG. 2 shows, as a side cross section view, tow 110 after it has beenexpanded, by means to be discussed later. The resultant expanded tow 110may be substantially wider than it is thick, thus forming a core.Between filaments 112 are large interstitial spaces 116, such that theentire expanded tow 110 has an open structure conducive to the transportof bodily fluids, as well as a soft feel due to the open, puffystructure.

FIG. 3 shows a side cross section of an absorbent core 210 according toone exemplary embodiment of the invention in which an expanded tow 110(FIG. 2) has been treated on one side with a superabsorbent material toafford a layer of that material over at least selected surfaces of thefilaments 218. The superabsorbent material, details of which will bediscussed below, is essentially free of particulate superabsorbentmaterial in this exemplary embodiment.

Treated filaments 218, indicated by broad lines, may be concentrated onone side of the absorbent core 210, while untreated filaments 212 are onthe other side, in the embodiment shown in FIG. 3. In order for there tobe sufficient absorbency in the core, at least about 5% of the totalcombined surface area of the filaments may be treated. Preferred is atleast about 50%, and still more preferred is at least about 80%.Although the treated filaments 218 are shown as each being completelycovered with superabsorbent polymer, some or all of them may be onlypartially covered. Also, although FIG. 3 shows two relativelywell-defined strata consisting of treated filaments 218 and untreatedfilaments 212 respectively, there may instead be a gradual transitionfrom one to the other across the thickness of absorbent core 210.Alternatively, all of the filaments may be treated with superabsorbentpolymer, which may be beneficial when maximum absorbency is desired.

Such an embodiment of the invention may help overcome a problem commonlyencountered in traditional absorbent articles, namely the phenomenon of“gel blocking”. In this situation, the otherwise porous structure of anarticle employing particulate superabsorbent polymers becomes occludeddue to swelling of the particles when they imbibe bodily fluids. Uponexposure to another flow of liquid, the article may not be able tohandle the additional demand quickly enough, and overflow occurs. Thismay result in leakage of fluid out of the article, wetting the wearer'sclothing.

When a fluid contacts the superabsorbent material in the embodimentshown in FIG. 3, the material swells. However, due to the open structurecreated by the interstitial spaces 216, gel blocking does not occur.Thus, when a second insult of liquid is applied to the core in use, theflow of liquid is not occluded. This diminishes the chances of fluidoverrunning an area of the article and wetting a user's clothing, whileat the same time ensuring that more nearly all of the superabsorbentmaterial is accessible to the fluid. This increases effective capacityfor fluid absorption.

According to an exemplary embodiment of the invention, treatment of theexpanded tow 110 to afford a layer of superabsorbent material isperformed by application of a liquid superabsorbent polymer. As usedherein, the term “liquid superabsorbent polymer” means one or moresuperabsorbent polymers at least partially dissolved in a liquidcarrier, or a solution in a liquid carrier of one or more superabsorbentprecursors, or a combination of one or more superabsorbent polymers andsuperabsorbent precursors. Such precursors include, inter alia, monomersthat are subsequently oligomerized, polymerized, and/or crosslinkedafter placement on a substrate to form superabsorbent polymers. It maysometimes be advantageous to include particulate superabsorbent polymersin such a formulation, for example if increased absorbency is desired.

Alternatively, using only nonparticulate materials may be preferred incases where it is desired to reduce shake-out of particulate matter, orshifting of absorbency within the article due to shifting of some of thesuperabsorbent particles. Both of these phenomena lead to inefficientsuperabsorbent polymer use, requiring the addition of moresuperabsorbent to compensate. These problems are largely avoided by theuse of liquid superabsorbent polymers, which attach more firmly to thesubstrate. The issues of shake-out and shifting are of particularimportance when tow is used in combination with particulatesuperabsorbents, because the spacing between fibers is much greater thanthat encountered in traditional cores employing pulp and superabsorbentpolymer particles. In these traditional systems, the pulp fibers helpkeep the superabsorbent particles in place to a greater degree than isthe case with expanded tow 110.

Numerous liquid superabsorbent polymers are known in the art.Nonlimiting examples of these, suitable for use with this invention,follow.

U.S. Pat. No. 4,944,963 to Dabi, incorporated herein by reference,describes forming a terpolymer of methyl methacrylate, acrylic acid, andglycidyl methacrylate, which is subsequently neutralized. The resultingsolution is applied to a fibrous substrate in the aqueous form. Excesssolution is removed by vacuum, and the treated substrate is heated for20 minutes at 120° C. to create a structure comprising substrate fiberson the surface of which is a crosslinked superabsorbent polymer.

U.S. Pat. No. 5,853,867 to Harada, incorporated herein by reference,describes a cationic absorbent polymer applied to a fibrous substrate asa monomer solution, with the monomer subsequently being polymerized onthe substrate by heating. Alternatively, preformed polymer may beapplied. Halogenated alkyl quaternary salts of dialkylamino(meth)acrylates are effectively used for the production of the polymers,and include the halogenated alkyl quaternary salts of such monomers asN,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-diethylaminobutyl (meth)acrylate,N,N-diethylaminoethyl (meth)acrylate, andN,N-diethylaminopropyl(meth)acrylate, for example. As used here, theterm “(meth)acrylate” means that either an acrylate or a methacrylate issuitable. Such a cationic absorbent polymer may be applied in a suitableliquid form such as, for example, by spraying or spreading a solution ofpolymer onto the substrate. Preferably, fixation of cationic absorbentpolymer to the substrate is attained by depositing a monomer or mixtureof monomers in the form of an aqueous solution on the substrate, andpolymerizing the monomers in the applied layer of monomer solution.

Another suitable liquid superabsorbent polymer is disclosed in U.S. Pat.No. 6,417,425 to Whitmore et al., incorporated herein by reference.There is described a sprayable composition comprising a monomer such asacrylic acid, methacrylic acid, and/or salts of these; a crosslinkersuch as ethoxylated and propoxylated trimethylolpropanetriacrylatederivatives (such as SR-9035 and SR-492, available from Sartomer Co.,Inc. of Exton, Pa.); and a polymerization initiator such as2,2′-azobis(2-(2-imidazole-2-yl))propane dihydrochloride, all in aqueoussolution. Also included in the composition are solid superabsorbentparticles. The mixture can be sprayed onto a fibrous substrate andsubsequently cured via heating or exposure to electron-beam orultraviolet radiation, to form a superabsorbent polymer matrix.

For the purposes of this invention, a liquid superabsorbent polymer maybe applied to the expanded tow 110 by any means known in the art.Examples of suitable means include spraying, dipping, and gravureapplication. A preferred method, in the case where it is desired tocover substantially all of the available filament surface, is tosubmerge the tow in a bath of liquid superabsorbent polymer (item 44 inFIG. 4), remove the tow from the bath, and remove excess liquidsuperabsorbent polymer by means of blowing with a jet of air, or severaljets. Such a method affords particularly facile and rapid coverage ofthe filaments.

Application may be performed such that an entire surface of theabsorbent core is treated, or may be performed in a pattern of treatedand untreated areas. Application may be from only one side or both sidesof the absorbent core, and may or may not extend through the entirethickness of the core.

The layer of superabsorbent polymer may be substantially continuous overthe surface of the filaments, rather than in discrete clumps, therebymaximizing the available surface area per unit weight of superabsorbentpolymer. In order to facilitate spreading of the liquid superabsorbentpolymer over the surface of the filaments, surface modificationtechniques such as for example corona discharge treatment may be appliedto the filaments. Alternatively, or in addition, the use of hydrophiliclubricants or surfactants may facilitate even distribution of the liquidsuperabsorbent polymer. Such methods are for example disclosed byPhillips et al in U.S. Pat. No. 5,972,505, where polyethyleneterephthalate filaments are treated with one of the following materials,all available from ICI Americas, Inc.:

-   -   Hypermer A109, a modified polyester surfactant    -   Brij 35, a polyoxyethylene (23) lauryl ether    -   Brij 99, a polyoxyethylene (20) oleyl ether    -   G-1300, a polyoxyethylene glyceride ester (nonionic surfactant)    -   G-1350, a polyoxyethylene-polyoxypropylene sorbitan linoleic        phthalic ester.

FIG. 4 shows an example of an overall process for preparing a core forincorporation into an absorbent article, according to the invention.Cellulose acetate or other tow is provided as a bale 41; the towconsists essentially of continuous filaments of fiber packed togetherinto a tight bundle. Tow 41 is fed into fiber spreader 42, where the towis spread apart by rollers to form a somewhat flattened shape. Thespread fibers are then fed into an air jet fiber opener 43, where thetow may be significantly opened up by turbulent, high-pressure air, forexample. Optionally, fibers such as pulp, cotton linters, pieces offilament, or other short fibrous material may also be incorporated intothe opened-up or expanded tow, for example by inclusion in the stream ofair from the air jet fiber opener, or by other means. Particulatesuperabsorbent polymer may also be introduced into the expanded tow inthis manner.

The opened-up tow may then be submerged in a bath 44 of liquidsuperabsorbent polymer, optionally also containing superabsorbentparticles. In the embodiment where tow is used without the addition ofshort fibers or particulate superabsorbent polymer by blowing in (orother means) as described above, there is reduced contamination of thebath with pieces of filament, since tow filaments are essentiallycontinuous. Submersion in this manner may afford a high and uniformloading of liquid superabsorbent polymer, penetrating through the entirecore. This may in some cases be advantageous, especially for thicker(higher basis weight) cores.

Alternatively, lighter and/or somewhat one-sided application may befavored for some applications. In such a case, application of the liquidsuperabsorbent polymer may instead be done for example by spraying, orby application using a gravure roller. Other means are known to thoseskilled in the coating art.

The process of FIG. 4 is particularly suitable for cases were theopened-up tow is of higher basis weight, for example in the range ofabout 30 gsm to about 500 gsm (grams/sq. meter), in order to achievemaximum penetration of the liquid superabsorbent polymer into the core.It may however be used for cores of any basis weight.

Excess liquid superabsorbent polymer may then be blown off of theexpanded tow using a compressed air source 45, for example, with theblown-off material being recycled back into the bath 44, reducingwastage of superabsorbent material. Air source 45 may be one or more airjets, and may be applied from one or both sides of the core, withvarious degrees of force or pressure. This may provide means for tuningor adjusting the loading profile of superabsorbent polymer as a functionof position in the core, i.e. to provide and/or adjust a gradient ofliquid superabsorbent polymer as a function of depth. Such adjustmentmay be designed to provide one or more strong gradients, or to minimizegradients and thereby give a more uniform profile of superabsorbentpolymer with depth.

The thus-coated filaments are then passed through a curing unit 46,which causes polymerization and/or crosslinking reactions to occur withthe reactive ingredients of the liquid superabsorbent polymer, therebyforming a superabsorbent polymer on surfaces of the filaments. Curingunit 46 may for example be a heating unit, an ultraviolet light source,or an electron beam source, as appropriate depending upon the type ofliquid superabsorbent polymer used.

The resulting “finished” tow is then passed through a dryer 47 to removewater and/or residual volatile reactants, and then into a tenderizingunit 48, which crimps and/or bends the coated filaments in order tosoften them, overcoming some of the stiffness imparted by the presenceof the superabsorbent layer. Finally, the resulting “soft-finished”coated tow may be fed into a rotary die cutter 49, where it is cut tosize to fit the dimensions of a desired absorbent article.

FIG. 5 shows an alternative process for preparing a core according tothe invention. A process generally like that described in relation toFIG. 4 is used, with the exception that application of the liquidsuperabsorbent polymer is performed with an upper sprayer 50 and a lowersprayer 52, which may afford coverage of both sides of the core andtherefore tend to improve penetration of the liquid superabsorbentpolymer into it, as compared to spraying on only one side. The method ofFIG. 5 may be particularly appropriate for lower basis weight cores, forexample those in the range of about 5 gsm to about 30 gsm. It mayhowever be used for cores of any basis weight. Air jets (not shown) mayalso be used either after applying the liquid superabsorbent polymer, orsimultaneously with it, to modify or adjust the distribution ofsuperabsorbent polymer in the core.

In another exemplary embodiment of the invention, the method detailed inFIG. 5 may be modified by eliminating one of sprayers 50 or 52. By usingsuch an approach, a core may be prepared in which superabsorbent polymeris concentrated on one side of the core, with little or nosuperabsorbent on the opposing side. The result of this is theformation, in a single structure, of regions that perform respectivelythe functions of absorbency and liquid transfer. Thus the opposing side,having little or no superabsorbent, may be placed nearer the user'sskin, and perform the function of an acquisition-distribution layer.This may obviate the need for a separate acquisition-distribution layer,but it may also be used In combination with such a separate layer. Airjets (not shown) may also be used either after applying the liquidsuperabsorbent polymer, or simultaneously with it, to modify or adjustthe distribution of superabsorbent polymer in the core.

Depending upon the amount of liquid superabsorbent polymer sprayed ontothe filaments, and the pressure of the spray as it impinges the core, itis possible to vary the total loading of the superabsorbent polymer andthe profile of its distribution through the thickness of the core. Thusfor example a relatively large amount of superabsorbent polymer sprayedat a high pressure will tend to result in deeper penetration into thecore. It will be readily appreciated that various combinations of sprayvolume and pressure will result in various gradients of superabsorbentpolymer loading through the thickness of the core, such that theabsorbency and other properties of the product can be tailored to meetparticular needs. Standard air jet nozzles and other equipment for suchspraying operations are well known, and spraying pressures may forexample vary from about 1 to about 100 PSIG (pounds/sq. inch, gage).

In yet another exemplary embodiment of the invention, referring again toFIG. 5, one of the sprayers 50 and 52 may apply a liquid superabsorbentpolymer while the other applies a surfactant solution. Thesurfactant-treated side of the core will thereby have increasedwettability, improving its ability to act as an acquisition-distributionlayer. Sufficient surfactant amount and spray pressure may be applied toallow significant surfactant to reach the opposite side, where theliquid superabsorbent polymer is applied, or conditions may be chosen toreduce such penetration, depending upon the needs of the particularabsorbent article to be produced. Air jets (not shown) may also be usedeither after applying the liquid superabsorbent polymer, orsimultaneously with it, to modify or adjust the distribution ofsuperabsorbent polymer and/or surfactant In the core.

The absorbent cores of the invention are particularly suitable forincorporation into absorbent articles for use in protectiveundergarments. Such a core may be used alone or in combination withanother core of similar construction, or one of a traditionalconstruction comprising for example kraft fluff and particulatesuperabsorbent polymer. Depending on cost, performance requirements,particular uses, and manufacturing considerations, various designs andmaterials of construction can be selected for use in assembling suchundergarments. U.S. Pat. No. 6,004,893 to Van Tilburg, which isincorporated herein by reference, describes a variety of such materialsand associated constructions.

For example, absorbent cores may be enwrapped with 17.1-gsm tissue fromCellu Tissue Corporation, East Hartford, Conn. The enwrapping tends toimprove wicking of fluid across more nearly the full width and length ofthe core. It may be C-folded around the core, or layered on top ofand/or below the core.

Absorbent cores may also be provided with a topsheet over the enwrapping(if used). The topsheet is liquid permeable and, when the article is inuse, is in close proximity to the skin of the user. If used, thetopsheet is preferably compliant, soft feeling and non-irritating to theuser's skin. Such topsheets can be made from any of the materialsconventional for this type of use, for example a 15.0 gsm spunbondpolypropylene nonwoven from Avgol Nonwoven Industries, located in Holon,Israel.

One particularly suitable material for the topsheet is for example a17-gsm wettable nonwoven coverstock, made of thermal bond polypropylene,available from PGI Nonwovens, Landisville, N.J. Other non-limitingexamples of suitable materials that can be used as a topsheet are wovenand non-woven polyester, polypropylene, polyethylene, NYLON, and RAYONand formed thermoplastic films. Suitable films are described, forexample, in U.S. Pat. No. 4,324,246 to Mullane and Smith and U.S. Pat.No. 4,342,314 to Radel and Thompson, both of which patents areincorporated herein by reference. Formed films may be selected for thetopsheet because they are permeable to liquids and yet non-absorbent.Thus, the surface of the formed film, which is in contact with the body,remains substantially dry and is more comfortable to the wearer.

If a topsheet is used, its inner surface may be secured in contactingrelation to the absorbent core. This contacting relationship results inliquid penetrating the topsheet faster than if it were not in contactwith the absorbent core. The topsheet can be maintained in contact withthe absorbent core by applying adhesive, optionally in spaced, limitedareas, to an inner surface of the topsheet. Examples of suitableadhesives used for this purpose include the acrylic emulsion E-1833BTmanufactured by Rohm and Haas Company of Philadelphia, Pa. and acrylicemulsions manufactured by H. B. Fuller Company of St. Paul, Minn. Alsocontemplated are thermoplastic hot melt adhesives such as 34-563A,available from National Starch, Inc.

Optionally, before a topsheet is applied, a fluid acquisition layer (notshown) may be attached adjacent and coextensive with the absorbent core,on the side of the core nearer the wearer, to improve distribution ofbodily fluid more evenly over the full width and length of the core. Atopsheet may then be affixed on top of the fluid acquisition layer. Sucha layer serves to manage, transport, accommodate and/or direct highvolumes and high flow rates of urine into the core. Thefluid-acquisition layer can be a through-air bonded/carded web, aspun-bond bi-component non-woven web, a web of cross-linked cellulosicfibers, apertured 3D film or the like. One particular suitable materialis available from PGI Nonwovens, Landisville, N.J., and has an overallbasis weight of 40 gsm, with high denier (10 denier) bi-component fiberssituated on the top (facing the topsheet) and low denier (6 denier)bi-component fibers situated on the bottom (facing the core). Thebi-component fibers are made of a polypropylene inner core andpolyethylene outer sheath. The fluid-acquisition layer may be adhesivelysecured in place by any suitable construction adhesive or hydrophilicadhesive, e.g. Cycloflex adhesive available from National Starch andChemical, Bridgewater, N.J.

In the exemplary embodiment of the invention shown in FIG. 3, wheretreated filaments are concentrated to one side of the core and untreatedfilaments predominate on the other side, the untreated side may itselfact to effectively distribute fluids, making the use of a separateacquisition layer unnecessary.

Crotch portions of protective undergarments employing an absorbent coreof this invention may comprise a barrier layer made of a material thatis impermeable to liquids and thus prevents bodily fluids and feces fromsoiling the clothing of the user. Any material used in the art for suchpurposes can be utilized herein. Suitable materials include, forexample, embossed or non-embossed polyethylene and polypropylene filmsand laminated tissue and non-woven materials.

Optionally, the impermeable barrier layer may be affixed substantiallycoextensive and parallel with the side of the absorbent core fartherfrom the wearer, to prevent wetting or soiling of clothing. Suitablebarrier layers may for example be a liquid-impervious laminatecomprising a soft nonwoven (cloth-like/hydrophobic) on the outside andfluid-impervious film (low gauge poly) on the inside. An example of thisis a poly laminate available from Clopay Plastic Products Company,Cincinnati, Ohio, which consists of 0.6 mil polyethylene film and 17 gsmSMS (spunbond/meltblown/spunbond) nonwoven. Another version is a polylaminate 9B-396 available from Pliant Corporation of Newport News, Va.,which consists of 0.3 mil copolymer film and 14 gsm SBPP (spunbondpolypropylene) nonwoven. However, other laminate variations may be usedin various gages and basis weights. For instance, other polymers(polypropylene, olefins, polyester, co-extruded polymers, etc.) orcoatings (adhesive, synthetic rubber, latex, polyurethane, etc.) can beused in place of the polyethylene film. Other material components(polypropylene, polyethylene, bi-component fibers, polyester, cotton,rayon, nylon, olefins, etc.) can be used in either woven or nonwoven(spunbond, thermal bond, through-air bond, etc.) construction in placeof the SMS outer cover. The preferred fluid-impervious film for theliquid-impervious laminate is a breathable 0.8 mil polyethylene version,which contains calcium carbonate, available from Tredegar Film Products,Richmond, Va. This material allows water vapor to pass through it, butdoes not permit the liquid itself to pass through it.

While preferred embodiments of the invention have been shown anddescribed herein, it will be understood that such embodiments areprovided by way of example only. Numerous variations, changes andsubstitutions will occur to those skilled in the art without departingfrom the spirit of the invention. Accordingly, it is intended that theappended claims cover all such variations as fall within the spirit andscope of the invention.

1. An absorbent core for use in an absorbent article, the corecomprising a plurality of substantially continuous and coextensivefilaments, at least some of the filaments having disposed on a surfacethereof a layer comprising a superabsorbent material formed in place onthe surface from a liquid superabsorbent polymer.
 2. The absorbent coreof claim 1, wherein the filaments are selected from the group consistingof RAYON, cellulose acetate, polypropylene, polyethylene, polyethyleneterephthalate, and sheath-core bi-component filaments, and combinationsthereof.
 3. The absorbent core of claim 1, wherein at least some of thefilaments comprise cellulose acetate.
 4. The absorbent core of claim 1,wherein the surface of at least some of the filaments is hydrophilized.5. The absorbent core of claim 1, wherein substantially all of thefilaments have disposed on said surface thereof said layer comprisingthe superabsorbent material.
 6. The absorbent core of claim 1, whereinthe core comprises two or more adjacent and coextensive strata, whereinone stratum comprises filaments having disposed on said surface thereofsaid layer comprising the superabsorbent material, and another stratumis substantially free of superabsorbent material.
 7. The absorbent coreof claim 6, wherein the another stratum comprises a surfactant disposedon the surface of at least some of the filaments.
 8. The absorbentarticle of claim 1, wherein the liquid superabsorbent material isselected from the group consisting of one or more superabsorbentpolymers at least partially dissolved in a liquid carrier, a solution ina liquid carrier of one or more superabsorbent precursors, and acombination of one or more superabsorbent polymers and superabsorbentprecursors.
 9. The absorbent core of claim 1, wherein the core has twoopposing sides and the superabsorbent material is disposed in a patternon one or both of the opposing sides.
 10. The absorbent core of claim 1further comprising pulp fibers Interspersed between at least some of thefilaments.
 11. The absorbent core of claim 1 further comprisingsuperabsorbent polymer particles interspersed among at least some of thefilaments.
 12. A method of making an absorbent core for use in anabsorbent article, the method comprising: a) expanding a tow comprisinga plurality of substantially continuous and coextensive filaments, eachfilament having a surface; and b) forming, from a liquid superabsorbentpolymer, a layer comprising a superabsorbent material on the surface ofat least some of the filaments.
 13. The method of claim 12 wherein theforming step comprises: applying to the expanded tow the liquidsuperabsorbent polymer to form a treated expanded tow comprising aliquid superabsorbent polymer coating; and curing the treated expandedtow to form the layer comprising the superabsorbent material.
 14. Themethod of claim 13 wherein the applying step comprises: immersing theexpanded tow in a bath comprising the liquid superabsorbent polymer;removing the expanded tow from the bath; and removing a portion of theliquid superabsorbent polymer coating.
 15. The method of claim 13wherein the applying step comprises spraying the liquid superabsorbentpolymer on at least one surface of the expanded tow.
 16. The method ofclaim 13 wherein the curing step comprises exposing the treated expandedtow to heat.
 17. The method of claim 13 wherein the curing stepcomprises exposing the treated expanded tow to radiation.
 18. The methodof claim 12, wherein the core has two opposing sides, and wherein theforming step comprises patternwise spraying the liquid superabsorbentpolymer on one or both of the sides.
 19. The method of claim 12, whereinthe core has two opposing sides, and wherein the forming step comprisesspraying the liquid superabsorbent polymer on one of the sides, themethod further comprising applying a surfactant to at least some of thefilaments on the other side.
 20. The method of claim 12 furthercomprising partially separating the filaments to form the expanded tow.21. The method of claim 20 wherein the step of partially separatingcomprises blowing the tow with jets of air.
 22. The method of claim 12further comprising at least partially flattening the tow.
 23. The methodof claim 12 further comprising interspersing pulp fibers between atleast some of the filaments.
 24. The method of claim 12 furthercomprising interspersing superabsorbent polymer particles between atleast some of the filaments.
 25. The method of claim 12 furthercomprising hydrophilizing at least some of the filaments.
 26. The methodof claim 12 wherein the forming step comprises forming a layer onsubstantially all of the filaments.
 27. The method of claim 12 furthercomprising, after the forming step, removing one or both of water andresidual volatile reactants from the formed layer.
 28. The method ofclaim 12 further comprising, after the forming step, tenderizing thefilaments having thereon said layer comprising the superabsorbentmaterial.
 29. A system for making an absorbent core for use in anabsorbent article, the system comprising: a) means for applying a liquidsuperabsorbent polymer to a tow comprising a plurality of substantiallycontinuous and coextensive filaments, thereby forming a treated expandedtow comprising a liquid superabsorbent polymer coating on the surface ofat least some of the filaments; and b) means for forming, from theliquid superabsorbent polymer coating, a layer comprising asuperabsorbent material on said surface of said at least some of thefilaments.
 30. The system of claim 29, wherein the means for applyingcomprises a bath.
 31. The system of claim 29, wherein the means forapplying comprises a spray nozzle.
 32. The system of claim 29, whereinthe core comprises two opposing sides, and wherein the means forapplying comprises a spray nozzle configured to apply the liquidsuperabsorbent polymer on one or both of the sides in a pattern.
 33. Thesystem of claim 29, wherein the core comprises two opposing sides, thesystem further comprising means for applying a surfactant to theexpanded tow.
 34. The system of claim 29, wherein the means for formingcomprises a heater.
 35. The system of claim 29, wherein the means forforming comprises a radiation source.
 36. The system of claim 29 furthercomprising means for removing a portion of the liquid superabsorbentpolymer coating.
 37. The system of claim 29 further comprising means forinterspersing pulp fibers between at least some of the filaments. 38.The system of claim 29 further comprising means for interspersingsuperabsorbent polymer particles between at least some of the filaments.39. The system of claim 29 further comprising means for flattening thetow.
 40. The system of claim 29 further comprising means for partiallyseparating filaments of the tow, thereby forming the expanded tow 41.The system of claim 40 wherein the means for partially separatingcomprises a source of air positioned to direct jets of air toward thetow.
 42. The system of claim 29 further comprising means for removingone or both of water and residual volatile reactants from the formedlayer.
 43. The system of claim 29 further comprising means fortenderizing the filaments having thereon a layer comprising asuperabsorbent material.